The present invention relates to the field of mass-storage devices. More particularly, this invention relates to a method and apparatus for detecting and recovering from head instability in a magneto-resistive (MR) transducer head.
Devices that store data are key components of any computer system. Computer systems have many different types of devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, circuitry that is used to write and/or read data to and from the disc via the transducer, and a bus interface to connect the disc drive into an information-handling system. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and receiving data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil or xe2x80x9cwrite headxe2x80x9d) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or xe2x80x9cread headxe2x80x9d) that detects changes in the magnetic field along the tracks for reading data. Some MR elements include giant magneto-resistive (GMR) technology.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information written on the disc(s) is used to accurately locate the transducer.
The transducer is also said to be moved to a xe2x80x9ctarget track.xe2x80x9d Once the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track in an operation called a xe2x80x9cseek.xe2x80x9d A seek is movement of an actuator assembly from a first track to a second target track. Acoustic emissions are more prevalent during rapid disc seek operations. To perform a seek, the actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
Nevertheless, each of these improvements have proved marginal, and some have been prohibitively costly. There is a need for a method and apparatus to substantially reduce unwanted acoustic emissions from the disc drive due to the actuator seeks and disc rotation. There is also a need for a method and apparatus to reduce the amount of vibration and shock absorbed into the disc drive from the external environment. There is also a need for an inexpensive method and apparatus.
A method and apparatus is described for recovering from a head-instability condition of a magneto-resistive (MR) transducer head.
One aspect of the present invention provides a disc drive. This disc drive includes a disc case, a disc rotatably mounted within the disc case, and an actuator assembly mounted within the disc case, the actuator assembly having a magneto-resistive (MR) transducer head. The disc drive also includes a controller and a current source. The current source supplies current to the MR head and is operatively coupled to be controlled by the controller to supply a nominal amount of current to the MR head when operating the MR head in a normal mode, and to supply one or more recovery current bursts having a current value above the nominal supply current in order to recover from a head-instability condition.
Another aspect of the present invention provides a head-instability-recovery circuit for use in disc drive to recover from a head-instability condition of a magneto-resistive (MR) transducer head. This circuit includes a controller and a current source that supplies current to the MR head. The current source is operatively coupled to be controlled by the controller to supply a nominal amount of current to the MR head when operating the MR head in a normal mode, and to supply one or more current bursts having a current above the nominal supply current in order to recover from the head-instability condition.
Yet another aspect of the present invention provides a method for recovering from a transducer-instability condition of a magneto-resistive (MR) transducer of a disc drive. This method includes (a) detecting a situation that indicates a head-instability-recovery operation is desired, and (b) performing the head-instability-recovery operation.
Still another aspect of the present invention provides a disc drive system that includes a base plate, a rotatable disc mounted to the base plate, an actuator, the actuator including a magneto-resistive (MR) transducer mounted to the actuator in transducing relation to the disc, and means as described herein, operably coupled to the MR transducer, for recovering from instability of the MR transducer.